Studies on needle blight disease of Blue pine (Pinus wallichiana Jack.) in Kashmir

Abstract

Studies were conducted on the etiology, epidemiology and management of needle blight of Blue pine (Pinus wallichiana) seedlings during 2008-2009 at Shalimar campus, Srinagar, Kashmir. The disease was prevalent in all the three surveyed districts of Kashmir viz. Anantnag, Baramulla and Srinagar with disease incidence of 31.11 and 28.83 per cent in nurseries and 42.85 and 35.84 per cent in plantations during 2008 and 2009, respectively. The average disease intensity in respective years in nurseries and plantations was 19.93 and 14.51 and 27.44 and 23.92 per cent, respectively. Lophodermium needle blight disease was characterized by the appearance of chlorotic patches which turned reddish brown with straw coloured centre surrounded by yellow halo. Infection at needle tip resulted in dieback. Severe infections caused the death of entire needle and premature defoliation. Characteristic black stromatic zone lines across the needle surface appeared in June-July. Fungal fructifications (pycnidia and hysterothecia) appeared on the infected intact and fallen needles during July to October. The hysterothecia with prominent longitudinal slits were usually formed on abaxial surface of needles. The Leptrostroma state (anamorph of Lophodermium pinastri) isolated in culture was unable to cause pathogenecity on both attached and detached Blue pine needles. The fungus proved pathogenic only when ascospore suspension was inoculated on Blue pine seedlings and detached needles. The pathogen associated with the disease on morphological characters was identified as Lophodermium pinastri Chiv. The pathogen exhibited maximum radial mycelial growth and pycnidial formation on PDA, Richards and Malt extract media. The host range of Lophodermium pinastri in various conifer plants revealed that all the conifer species (Pinus wallichiana, P.halepensis, Abies pindrow, Cedrus deodara, Cuprussus torulosa, Picea smithiana and including one Cryptomeria species) reacted positively except Thuga orientalis. The ascospore release and germination of Lophodermium pinastri under in vitro conditions varied significantly at different test temperatures with highest ascospore release and germination at 25°C. The ascospore release occurred in relative humidity regimes of 60 to 100 per cent only with highest ascospore release and germination at 100 per cent RH. The disease appeared in February and reached maximum by the end of October. During the study period maximum logrithemic infection rate of 0.0618 and 0.0285 unit/day was recorded during the first fortnight of April in 2008 and 2009, respectively. Weather factors viz. temperature and relative humidity were positively correlated with disease intensity (62.1 per cent contribution). However, except temperature all other weather factors were positively correlated with the disease development in terms of infection rate (units/day) (25.7 per cent contribution). The pathogen perpetuated in the form of pycnidia and hysterothecia on fallen diseased needles. The fungal fructifications (pycnidia and hysterothecia) and their viability decreased with increase in the depth of placement in forest litter. Maximum fructifications on pine needles were observed at ground surface (0 cm depth). The diseased needles kept at 0 cm litter depth exhibited maximum hysterothecial formation and ascospore production and greater viability. Conidiomatal formation and conidial production of L. pinastri occurred in the 2nd fortnight of August and in 1st fortnight of September in the year 2008-2009 and 2009-2010, respectively. However, hysterothecial formation, ascospores production and their viability decreased significantly with increase in burial depth in forest litter. Non-systemic fungitoxicants, tested at various concentrations significantly inhibited the mycelial growth and ascospore germination of the pathogen by 52.31 to 76.34 and 60.50 to 82.21 per cent, respectively. Hexaconazole 5 EC proved superior over all other systemic fungitoxicants tested followed by flusilazole 40 EC and carbendazim 50 WP. The studies on in vivo evaluation of most effective fungitoxicants under mist- and poly-chamber conditions at three relative humidity regimes revealed that disease incidence and intensity were comparatively higher in mist- than in poly-chamber. In both, mist- and poly-chambers the Blue pine seedlings treated with hexaconazole 5EC (@ 0.03%) or carbendazim 50WP (@ 0.1%) treated seedlings had significantly less disease incidence and intensity. Increase in humidity regime from 60 to 100 per cent significantly enhanced needle blight disease incidence and intensity. All the fungitoxicants used as either single spray or protectant followed by systemic fungitoxicant spray significantly reduced the disease incidence and intensity as compared to check. The mean disease intensity in fungitoxicant treated Blue pine plants varied from 3.68 to 11.70 per cent as compared to 26.66 per cent in check. Among the fungitoxicants tested mancozeb 75 WP (@0.3%) followed by 2nd spray with carbendazim 50 WP (@0.1%) or hexaconazole 5EC (@0.03%) proved superior in reducing the disease incidence and intensity on Blue pine plantations or spraying with chlorothalonil 75WP (@0.3%) followed by 2nd spray with carbendazim 50 WP (@0.1%) or hexaconazole 5EC (@0.03%) was effective in minimizing disease incidence and intensity. Two-spray treatments exhibited lesser disease intensity (3.68-5.71%) and no defoliation as compared to mono-sprayed treatments which exhibited disease intensity of 8.64 to 11.70 per cent and defoliation of 1 to 10 per cent. Electrolytic leakage in infected blue pine needles was monitored by measuring the conductivity change in pine needles affected by Lophodermium needle blight disease. Highest electrolytic leakage of 345.33 µmoh/cm was noticed in pine needles having > 81 per cent of disease severity in comparison to unaffected check (181.33 µmoh/cm)